I use the Logitech Driving Force Ex wheel with GIMX to play GT Sport on the PS4 (I'm actually the guy who uploaded the first Driving Force Ex config here). I've recently noticed that some cars have different steering sensitivities.

There's a little red dot at the bottom of the screen in GT Sport that indicates steering input. When I use a certain category of cars (gr4) the little red dot that indicates steering input goes fully to the left a lot sooner than when I use a different category of cars (gr3) cars even when I'm using the EXACT SAME axis sensitivity in the GIMX config file. If I make it so that I can use the full range of the wheel on gr3 cars (the red dot goes fully left when turning 100° to the left since this is a 200° wheel), I can only turn about 60° degrees left on a gr4 car before the dot goes fully left. So I have to decrease axis sensitivity on my GIMX every time I change from gr3 to gr4 and increase it every time I go from gr4 to gr3.

This doesn't happen when using a controller, so I don't think it is only a game-related issue. I even asked some players that use officially supported wheels and they also told me that this doesn't happen on their wheels. But one of my friends who uses a Fanatec wheel told me that he also noticed this and it's because the Fanatec also emulates the G29 ingame. So I was wondering if there's anything you could do to fix this?

Another thing that annoys me, and I already complained about this here, is that if I set it up so that I can use the full range of the wheel, the cars just don't turn on slow corners such as the Suzuka hairpin, Nurburgring GP turn 1, Monza chicane... The first solution I found was to adjust the axis sensitivity while driving for every corner separately but that was not ideal because I kept spinning out a lot. I now use a way higher axis sensitivity, but this also isn't ideal because now I can only use the middle <>50° of rotation before max steering lock is achieved ingame. I have no idea what can be done about this tho.

I already have to change profiles between races. I was asking if you could do anything about it because it takes up 3 buttons on my wheel for each profile that I'd rather be using for something else, and I can't use the keyboard to do that because about 10 minutes after starting up GIMX it starts ignoring the keyboard for some reason (another issue possibly?).
I tried playing around with acceleration and sensitivity yesterday. I tried a very low sensitivity with a high acceleration and the problem was still there. Then I tried a very high sensitivity with acceleration below 1. Still the same problem. I'm not sure what acceleration does anyway, it seems to me it just acts like a multiplier to sensitivity as the output always seemed linear.
I don't know what you meant by "0-50% in -> 0-30% out, 50%-100% in -> 30-100% out" and I also couldn't figure that out from the post you suggested?
And I'm not buying another old wheel. If anything I'm getting the T300 or something new. My current one wobbles a lot when going straight (this probably isn't a GIMX problem because it also happens when I play on PC) plus it's 10 years old so I think it's finally time for an upgrade.

You can define the same button as trigger for different profiles. The first profile is active on startup. Pressing the trigger activates the next profile. When the last profile is active pressing the trigger activates the first profile.

Acceleration is definitely not a multiplier. Look at the spreadsheet attached to the post linked earlier.
"0-50% in -> 0-30% out, 50%-100% in -> 30-100% out" means that 50% of the turning range (input) controls 30% of the output range, and that the remaining 50% of the turning range (input) controls 70% of the output range.

Thanks for the tip, didn't know that I could define the same button for different profiles.

I'm now beginning to understand acceleration and the spreadsheet and what it all means. But the thing is, my wheel doesn't exactly behave like that in reality. For example, when I use the default 0.004 wheel sensitivity with 1.00 acceleration, it reaches 100% output at about 40% input in-game whereas the spreadsheet with the same settings is barely above 0% output even at 100% input. Am I misunderstanding something? Do I have to edit something else in the spreadsheet?

Correction: After further inspection, it seems that when I use the default 0.004 wheel sensitivity with 1.00 acceleration, the red dot goes fully to the left at 40% input (about 40°) but this is not actually 100% output. If I then turn the wheel all the way the red dot is still fully to the left but the car can turn more (=has a shorter turning radius and I can drive around tight corners faster). This is actually the same problem I described when I first posted this. The ingame red dot is completely out of sync from the input and the output (how the car actually behaves).

Because of this and the fact that there seems to be something wrong with the sensitivity calculator spreadsheet, it's really hard to find an optimal steering sensitivity and acceleration for my wheel. I have no idea at what point 100% output is actually achieved. Also, the default sensitivity is way too sensitive for my wheel in the middle. Should I use the default sensitivity with acceleration below 1? Or should I use a low sensitivity and high acceleration?